1. Field of the Invention
The present invention relates to a zoom lens mechanism suitable for use with a zoom lens system such as that proposed by the assignee of the present application in U.S. patent application Ser. No. 09/534,307 (Japanese Patent Application No. Hei 11-79572).
2. Description of the Related Art
In a zoom lens system of the prior art, there are contradictory demands for a high zoom ratio and miniaturization. For example, in a two-lens-group zoom lens system which can be miniaturized, if the paths of the lens groups thereof (hereinafter, zoom paths) are determined (i.e., solutions for zoom paths) so that the zoom ratio becomes high, interference of the lens groups occurs on the telephoto side, or interference of a lens group and the image plane occurs on the wide-angle side. On the other hand, in a three-lens-group zoom lens system, the zoom ratio thereof can be made higher than that of a two-lens-group zoom lens system; however, miniaturization is difficult. Furthermore, if an attempt is made to obtain a higher zoom ratio, and if the power of these three lens groups is determined accordingly, precision on the operations of the zoom lens system cannot be obtained due to the mechanical structure thereof.
The assignee of the present application has proposed an unprecedented zoom lens system that meets the contradictory demands of high zoom ratio and miniaturization (U.S. patent application Ser. No. 09/534,307). This zoom lens system has the following characteristics: it includes a plurality of movable lens groups for varying the focal length; at least one of the lens groups is a switching lens group which includes two sub-lens groups, one of the sub-lens groups being a movable sub-lens group that can be selectively positioned at either one movement extremities in the optical axis direction with respect to the other sub-lens group; the movable sub-lens group of the switching lens group is positioned at an extremity of a short-focal-length zooming range, from the short focal length extremity to an intermediate focal length, and at the opposite extremity of a long-focal-length zooming range, from the intermediate focal length to a long focal length extremity; and zoom paths of the switching lens group and the other lens groups are discontinuous at the intermediate focal length and are defined to focus on a predetermined image plane corresponding to the position of the movable sub-lens group. There may be one or more intermediate focal lengths.
Accordingly, it is an object of the present invention to provide a lens mechanism (lens barrel) suitable for use with a zoom lens system that includes the switching lens group as described above.
In order to achieve the above-mentioned object, a zoom lens mechanism for moving a switching lens group of a zoom lens system is provided, the switching lens group constituting one of a plurality of variable lens groups of the zoom lens system, which moves in an optical axis direction upon zooming, and including first and second sub-lens groups, wherein the first and the second sub-lens groups serves as a focusing lens group in a mutually close position and in a mutually distant position in the optical axis direction. The zoom lens mechanism including a switching lens group frame supporting a first sub-lens group frame and a second sub-lens group frame in a manner that allows relative rotation and linear movement in the optical axis direction of the first and second sub-lens groups, the first and second sub-lens group frames supporting the first and the second sub-lens groups, respectively; a lens group shift mechanism for causing the first and second sub-lens group frames to move to the mutually close position and the mutually distant position, in accordance with relative rotation between the first sub-lens group frame and the second sub-lens group frame; and a focusing mechanism which integrally moves the first sub-lens group frame and the second sub-lens group frame in the optical axis direction while maintaining a distance between the first and the second sub-lens group frames after the first and the second sub-lens group frames are moved to one of the mutually close position and the mutually distant position by the lens group shift mechanism.
Preferably, an actuator ring is rotatably provided in the switching lens group frame and is rotated to cause the lens group shift mechanism and the focusing mechanism to operate.
Preferably, the actuator ring is rotatable in one and the other direction over a predetermined angular range. The lens group shift mechanism includes a shift cam mechanism provided on opposed surfaces of the first sub-lens group frame and the second sub-lens group frame. The second sub-lens group frame is rotatable in one and the other direction via the corresponding rotation of the actuator ring. The first sub-lens group frame is supported within the switching lens group frame so as to be linearly movable in the optical axis direction and so as not to be relatively rotatable with respect to the second sub-lens group frame.
Preferably, the shift cam mechanism includes a shift cam surface which is formed on one of the opposed surfaces of the first and second sub-lens group frames, the shift cam surface being inclined with respect to a plane normal to the optical axis; and a follower projection which is formed on the other of the opposed surfaces, the follower projection engaging with the shift cam surface.
In an embodiment, the actuator ring is rotated from one rotation extremity to the other rotation extremity to linearly move the first sub-lens group frame to one of the mutually close position and the mutually distant position, the second sub-lens group frame relatively rotating in one direction with respect to the first sub-lens group frame, wherein the second sub-lens group frame is thereafter rotated in the other direction in order to carry out a focusing operation. The focusing mechanism includes a focus cam mechanism formed on opposed surfaces of the actuator ring and the second sub-lens group frame so that the rotation of the actuator ring in the other direction causes the second sub-lens group frame to move one of forwardly and rearwardly in the optical axis direction.
Preferably, a pair of rotation preventing surfaces are provided between the switching lens group frame and the second sub-lens group frame, the pair of rotation preventing surfaces defining rotational movement extremities of the second sub-lens group frame, which is rotated via the actuator ring, for one and the other direction.
The focus cam mechanism carries out a focusing operation in accordance with the rotation of the actuator ring in one and the other direction, relative to a reference position which corresponds to one of the pair of the rotation preventing surfaces.
Preferably, the focus cam mechanism includes a pair of effective surfaces and a pair of focus cam surfaces formed on the actuator ring, wherein the pair of effective surfaces are spaced apart from one another in a circumferential direction, and the pair of focus cam surfaces extend between the pair of effective surfaces, the pair of focus cam surfaces having opposite slopes with respect to a plane normal to the optical axis; and a lug which is formed on the second sub-lens group frame, the lug comes into contact with at least one of an effective surface of the pair of effective surfaces and the focus cam surface.
Preferably, the pair of focus cam surfaces of the actuator ring are symmetrical with respect to a center line which extends in between the pair of the effective surfaces in a direction parallel to the optical axis.
Preferably, the lug of the second sub-lens group frame includes a pair of contact surfaces which are circumferentially apart from each other and respectively come into contact with each of the pair of effective surfaces; and a circular end surface which comes into contact with the focus cam surface.
According to another aspect of the present invention, a zoom lens mechanism for moving a switching lens group of a zoom lens system is provided, the switching lens group constituting one of a plurality of variable lens groups of the zoom lens system, which moves in an optical axis direction upon zooming, and including first and second sub-lens groups, wherein the first and the second sub-lens groups serves as a focusing lens group in a mutually close position and in a mutually distant position in the optical axis direction. The zoom lens mechanism including a switching lens group frame supporting a first sub-lens group frame in a manner that allows linear movement of the first sub-lens group frame in the optical axis direction and prevents relative rotation thereof, and supporting a second sub-lens group frame in a manner that allows rotation thereof over a predetermined angular range and allows linear movement thereof in the optical axis direction, the first and second sub-lens group frames supporting the first and the second sub-lens groups, respectively; an actuator ring for rotating the second sub-lens group frame in one and the other direction over the predetermined rotation range, the actuator ring being supported in the switching lens group frame in a manner that prevents linear movement of the second sub-lens group frame in the optical axis direction and allows rotation thereof in the one and the other direction; a lens group shift mechanism that causes the first sub-lens group frame and the second sub-lens group frame to move to one of the mutually close position and the mutually distant position, with respect to the optical axis direction, as the actuator ring rotates the second sub-lens group frame in one and the other direction, respectively; and a focusing mechanism which moves the first sub-lens group frame and the second sub-lens group frame in the optical axis direction while maintaining a distance between the first and the second sub-lens group frames after the first and the second sub-lens group frames are moved to one of the mutually close position and the mutually distant position by the lens group shift mechanism.
Preferably, the switching lens group frame is provided with a linear guide mechanism for guiding the second sub-lens group frame in the optical axis direction without rotating when the focusing mechanism linearly moves the first and the second sub-lens group frames.
Preferably, the lens group shift mechanism includes a shift cam mechanism which includes a shift cam surface formed on one of the opposed surfaces of the first and second sub-lens group frames, the shift cam surface being inclined with respect to a plane normal to the optical axis; and a follower projection formed on the other of the opposed surfaces for engaging with the shift cam surface.
In an embodiment, the actuator ring is rotated from one rotation extremity to the other rotation extremity to linearly move the first sub-lens group frame to one of the mutually close position and the mutually distant position, the second sub-lens group frame relatively rotating in one direction with respect to the first sub-lens group frame, wherein the second sub-lens group frame is thereafter rotated in the other direction in order to carry out a focusing operation. The focusing mechanism includes a focus cam mechanism formed on opposed surfaces of the actuator ring and the second sub-lens group frame so that the rotation of the actuator ring in the other direction causes the second sub-lens group frame to move one of forwardly and rearwardly in the optical axis direction.
Preferably, a pair of rotation preventing surfaces are provided between the switching lens group frame and the second sub-lens group frame, the pair of rotation preventing surfaces defining rotational movement extremities of the second sub-lens group frame, which is rotated via the actuator ring, for one and the other direction.
The focus cam mechanism carries out a focusing operation in accordance with the rotation of the actuator ring in one and the other direction relative to a reference corresponding to one of the pair of the rotation preventing surfaces.
Preferably, the focus cam mechanism includes a pair of effective surfaces and a pair of focus cam surfaces formed on the actuator ring, wherein the pair of effective surfaces are spaced apart from one another in a circumferential direction, and the pair of focus cam surfaces extend between the pair of effective surfaces, the pair of focus cam surfaces having opposite slopes with respect to a plane normal to the optical axis; and a lug which is formed on the second sub-lens group frame, wherein the lug comes in contact with at least one of the effective surface of the pair of effective surfaces and the focus cam surface.
Preferably, the pair of focus cam surfaces of the actuator ring are symmetrical with respect to a center line which extends in between the pair of the effective surfaces in a direction parallel to the optical axis.
Preferably, the lug of the second sub-lens group frame includes a pair of contact surfaces which are circumferentially apart from each other and respectively come into contact with each of the pair of effective surfaces; and a circular end surface which comes into contact with the focus cam surface.
According to another aspect of the present invention, a zoom lens mechanism for moving a switching lens group of a zoom lens system is provided, the switching lens group constituting one of a plurality of variable lens groups of the zoom lens system, which moves in an optical axis direction upon zooming, and including first and second sub-lens groups, wherein the first and the second sub-lens groups serves as a focusing lens group in a mutually close position and in a mutually distant position in the optical axis direction. The zoom lens mechanism includes a switching lens group frame supporting a first sub-lens group frame and a second sub-lens group frame in a manner that allows relative rotation and linear movement of the first and second sub-lens group frames in the optical axis direction, the first and second sub-lens group frames supporting the first and the second sub-lens groups, respectively; an actuator ring that is retained in the switching lens group frame in a manner that allows rotation of the actuator ring in one and the other direction; a shift cam mechanism for causing the first and second sub-lens group frames to move to one of the mutually close position and the mutually distant position, in the optical axis direction, in accordance with relative rotation between the first sub-lens group frame and the second sub-lens group frame; and a focus cam mechanism which moves the first sub-lens group frame and the second sub-lens group frame in the optical axis direction while maintaining a distance between the first and the second sub-lens group frames after the first and the second sub-lens group frames have are moved to one of the mutually close position and the mutually distant position by the shift cam mechanism. The actuator ring is rotated from one rotation extremity to the other rotation extremity to rotate the second sub-lens group frame in one direction so that the shift cam mechanism causes the first sub-lens group frame to move to one of the mutually close position and the mutually distant position, with respect to the second sub-lens group frame, and thereafter the actuator ring is rotated in the other direction for focusing. The focus cam mechanism causes the first sub-lens group frame and the second sub-lens group frame to move one of forwardly and rearwardly, in the optical axis direction, as a result of the rotation of the actuator ring in the other direction, in order to carry out focusing.
Preferably, the shift cam mechanism is provided on opposed surfaces of the first sub-lens group frame and the second sub-lens group frame.
Preferably, the focus cam mechanism is provided on opposed surfaces of the actuator ring and the second sub-lens group frame.
The present disclosure relates to subject matter contained in Japanese Patent Application No. 2000-288546 (filed on Sep. 22, 2000) which is expressly incorporated herein by reference in its entirety.